I assume you are asking about production models that were for sale to the public, and not concept/expermintal tractors.
If so, the production model that I would like is an Oliver Hart Parr standard row crop (sugar cane model) built in 1930 or 1931. I have only see one.
My second choice would ba a Oliver Twin 880. I have never see one in person, but there were six built and one sold.